“违反诺言”常见的英文表达是 “break one's promise” 。
例句：
He broke his promise and never came back to see me again.（他违反了诺言，再也没有回来看我。）
It's not right to break your promise just because it's inconvenient for you.（仅仅因为对你来说不方便就违反诺言是不对的。）
此外，也可以用 “go back on one's promise” 来表达相同意思。
例句：
She went back on her promise and refused to help us.（她违反了诺言，拒绝帮助我们。）